The present invention relates to monitoring one or more conditions of pneumatic tires mounted on wheels. As a rotary element, a tire's angular position, rotational (angular) velocity and acceleration, rate of change of acceleration, and revolution count are important in determining such things as vehicle and/or tire instantaneous position, speed, mileage, acceleration and braking, slip/skid, and are also factors in the wear of the tire.
In addition to rotational/angular characteristics, other important characteristics to be monitored in a pneumatic tire are pneumatic pressure and temperature. Pressure (pneumatic pressure) is well known as a critical factor in pneumatic tire operation, most importantly if there is a loss of sufficient pressure to safely operate the tire, e.g., a “flat tire”. The (pneumatic) temperature is generally of secondary importance. Although it can be used to indicate an average temperature of the tire and wheel surrounding the pneumatic cavity, temperature is mostly used to normalize a pressure measured in a hot tire to a “cold pressure” value, i.e., the pressure as it would be in a “cold” tire.
A great deal of prior art is devoted to apparatus and methods for measuring and monitoring pneumatic tire conditions. U.S. Pat. No. 3,665,387 discloses a low tire pressure warning system adaptable for any number of wheels of a vehicle and providing dashboard indications of system operation and low pressure conditions while the vehicle is in motion.
U.S. Pat. No. 4,911,217 discloses an RF transponder in a pneumatic tire. FIG. 1a of this patent illustrates a prior-art identification system (“reader”) that can be used to interrogate and power the transponder within the tire. U.S. Pat. No. 5,181,975 discloses a pneumatic tire having an integrated circuit (IC) transponder and pressure transducer. As described in this patent, in a tire that has already been manufactured, the transponder may be attached to an inner surface of the tire by means of a tire patch or other similar material or device.
Dynamic conditions such as position and angular velocity of a rotary element are readily measured. Straightforward tire revolution counters are well known, represented by way of example in U.S. Pat. Nos. 4,842,486 and 5,524,034. U.S. Pat. No. 5,218,862 discloses a tire pressure monitor comprising wheel speed sensors located at the vehicle's wheels to convey wheel speed information to an electronic controller. This patent notes that the wheel speed discrepancy between one tire to the others indicates the relative tire pressure, but that discrepancy may also be indicative of the vehicle turning, accelerating or decelerating, going up or down steep grades, or of one wheel slipping, or of a cross wind bearing on the vehicle.
From the foregoing, it is thus known to put transponders (and associated sensors) in pneumatic tires of motor vehicles. These transponders transmit a RF wave, with or without variable data (e.g., tire pressure, temperature, position) and/or fixed data (e.g., tire ID) to outside the tire, and receive RF signals, with or without data, from outside the tire. A separate transponder is typically associated with each tire of a motor vehicle to monitor and transmit tire-related data. Typically, an “interrogator” having both transmitting and receiving capabilities is used to communicate with the transponders.
Such systems heretofore have been implemented primarily in passenger vehicle applications for the purpose of monitoring tire conditions such as pressure and temperature and communicating such information to the vehicle operator. Safety has been a primary consideration in such implementations. Application of such systems in tires for farm or agricultural vehicles has not, however, generally occurred. Accordingly, heretofore little attention and emphasis has been placed on creating expanded applications using pneumatic tire information generated from the implementation of tire monitoring systems in a farm tire.
In farm vehicle applications, certain systems for measuring tire rotational speed have been applied as inputs to the vehicle's electronic control unit, typically a microprocessor. Such speed measuring systems are radar systems that are expensive to implement and maintain and cannot be used for other purposes such as storage of new tire information or for measuring tire parameters such as air pressure and temperature. There remains, therefore, a need in the industry for an inexpensive means for providing inputs to engine management systems that may be used for myriad agriculture applications. Moreover, such a system should be flexible and provide means for the storage of new tire information and for measuring other tire parameters such as air pressure and temperature. Still further, an ideal solution to the needs of the industry can be capable of use by OEM's as a main input directly into a vehicle's electronic control unit and be capable of use by a tire maker to store relevant information about the tire such as its Date Code, tire specification; and a tire identification tied to tire uniformity.